Ligaments are elongated bands of collagenous connective tissue which interconnect bones and stabilize the movement of bones relative to one another. Each end of a ligament is affixed to a bone. Torn ligaments, particularly in the knee, ankle and shoulder, are common injuries among athletes and frequently require extensive reconstruction or replacement.
Unlike vascular tissue, such as bone and skin, torn or damaged ligaments do not naturally heal because they are not vascularized, i.e., they are not supplied with a network of blood vessels which provide blood and lymph for tissue regeneration and repair. Thus, they must either be repaired, if possible, or replaced with a substitute material which will simulate the biomechanical properties of the original ligament. Surgical repair of a tom ligament, such as by mending, does not restore full strength and elasticity to the ligament and is thus of limited benefit. On the other hand, surgical replacement of a torn or damaged ligament with a natural or artificial prosthesis can substantially restore normal patient activity levels and is frequently prescribed. However, in the case of replacement with a natural or synthetic substitute, the replacement ligament must be affixed to the respective bones in a manner permitting substantially similar function to the original ligament.
The anterior cruciate ligament (ACL) connects the femur and the tibia within a knee joint. The ACL is the single most important stabilizing structure within the knee: it limits the movement of the bones of the joint and resists anterior displacement of the tibia with respect to the femur at all flexion positions. The ACL also resists forces which tend to hyperextend the knee.
Ruptures of the anterior cruciate ligament are among the most common injury to the knee. It is estimated that half a million ACL reconstructions are performed per year in the United States alone, with that number doubling for ACL reconstructions worldwide. Reconstruction of the ACL is a highly demanding procedure involving a determination of the correct anatomic location for an ACL substitute, the location and preparation of bony tunnel sites for the ACL substitute, and proper in situ fixation and tensioning of the ACL substitute.
One of the most widely used ACL substitutes is the bone-patellar tendon-bone (BPTB) graft. The term "graft", as used herein, refers to a natural or synthetic implantable substitute for various kinds of tissue. The central one-third of the patient's or a donor's patellar tendon, along with portions of the bony insertions of the patellar tendon, are used as a replacement for the damaged ACL. The bony insertions are preferably harvested as cylindrical bone plugs to facilitate implantation and fixation of the BPTB graft into osseous tunnels of the patient's knee joint. The BPTB graft is a popular choice for ACL reconstructive surgery because of its high load strength and its superior bone fixation properties.
Another commonly used ACL substitute is the iliotibial band (ITB) graft. The ITB is a section of ligament which can be harvested from a portion of a patient's or a donor's iliotibial ligament located within the anterolateral ligament structures of the knee joint.
Generally, to use such BPTB or ITB grafts, an osseous tunnel is established in both the femur and tibia of a patient, and the bone plugs of the BPTB graft, or the ends of the ITB graft, are positioned within, and affixed to, the tunnels, with a predetermined tension and angular orientation established in the tendon. In order to promote effective fusion of the bone plugs of a BPTB graft to the side walls of the osseous channels, a close fit, and preferably direct contact, is desired. It is also important, from a functional standpoint, to have a specific tension in the ligament when it is anchored in place.
Identification of the optimal location and tension of such a graft and, once identified, accomplishing the identified location and tension, are difficult tasks. Generally, the surgeon lacks adequate equipment for precisely determining the appropriate anatomic location for correct placement of the graft, for preparing the bony tunnel sites, and for anchoring and tensioning the graft, and often a limited trial-and-error approach is used.
Various devices for fixing ligaments and ligament substitutes to bone are known. For example, U.S. Pat. No. 4,537,185 to Stednitz discloses a self-drilling, self-tapping cannulated fixation screw which can be inserted over a guide wire and positioned in a desired location within a bone. Such bone screws are commonly used as graft fixation devices for the bone plugs of BPTB grafts. In such cases, a bone screw is inserted into the interfacial space between the bone plug at the graft and the wall of the osseous tunnel to establish an interference fit. Although this approach may effectively secure the bone plug in the channel ligament, the screw necessarily creates a gap on one side of the plug while driving the other side of the bone plug against the sidewall of the tunnel. This less-than-360 degree contact is less than optimal.
Other fixation devices employ various structures for coupling with a ligament or a suture and for engaging with the bone. For example, U.S. Pat. No. 5,356,435 to Thein discloses an element for fixing a ligament in a bony canal. The element includes an internal conduit for receiving an end of a ligament, and a clamping structure for securing the ligament end within the conduit. U.S. Pat. No. 5,356,413 to Martins et al. discloses a surgical anchor having a body portion and a suture-receiving bore. The body portion includes a rearward portion adapted for receiving a ligament, and a plurality of barbs extending outwardly and rearwardly from the body for engaging with the walls of a bony tunnel in a force fit.
None of these fixation devices permits a surgeon to easily fix the fibrous or bony portions of a ligament substitute in a desired position within a bony tunnel (e.g., in full 360-degree contact with the channel walls) and also establish the desired tension and angular orientation in the ligament substitute in situ. The grafted ligament substitute which is fixed with these devices may loosen under load as a result of the asymmetric positioning of the fixation device in the bony tunnel with respect to the graft and the forces on the joint. Also, torque applied to a bone screw to fix a graft may be undesirably transferred to the graft itself, thereby changing the orientation of the ligament substitute in the bony tunnel. Also, if removal of the bone screw is required, it must be either unscrewed or chipped out, leaving an untilled hole in the bone. Also, some fixation devices are relatively large in cross-section, requiring a bony canal of relatively large diameter. Damaged or diseased host tissue may not be sufficiently strong or extensive to permit the use of large fixation devices therein.
It is therefore an object of the present invention to provide a graft fixation device which obviates the disadvantages of the prior art devices.
It is another object of the present invention to provide a graft fixation device which can establish in situ a desired tension in a ligament graft.
It is another object of the present invention to provide a graft fixation device which can establish in situ a desired axial position for a ligament graft.
Yet another object of the present invention to provide a graft fixation device which can also be used to rotate a ligament graft in situ about its longitudinal axis to achieve a desired angular orientation or create a desired spiral twist in the graft.
It is another object of the present invention to provide a graft fixation device which is minimally invasive to a patient.